I have some upcoming travel where I am planning to do some hiking/trail running. I am hoping someone could recommend to me an app that can use the GPS in my phone to help me navigate trails where there is no cell service. The easier (read: apps for dummies) to use, the better!
As far as I’ve been able to tell, OnTheGoMap has fine data for distance and elevation when mapping roads—it relies on OpenStreetMap data. A little less so with trails because the trails that OnTheGoMap knows about don’t always match what I know to be true in the real world, so distance accuracy will suffer then. The same is true if you have to guess at where a trail is. Elevation accuracy is likely to be good at all times because the mapping data should be decent everywhere. The main issue there is bridges, which throw things off weirdly.
I really like OnTheGoMap, and had thought to use it as the basis for the Two Hollows Monster Marathon and Half website, but found that it measured the course a half-mile short of 13.1 miles compared to GPS measurements made by several runs encompassing various runners and various watches, all of which agreed quite closely with one another. So you can probably consider OnTheGoMap’s distances in the right ballpark but somewhat approximate.
The comparison between GPS watches and online maps is a tricky one. We tend to take for granted that GPS watches are accurate since they’re what we use every day. And to some extent, they’re truth for us—it doesn’t really matter whether or not they’re precisely accurate because that’s what we think we’re running. And a half mile here or there isn’t important.
However, when I was creating the RunGo directions for the Lick Brook & Treman FLT course for the FLRC Challenge last year, I was starting from @Petorius’s GPS track from running it, which was a bit longer than the believed 13.1 miles. What I found upon zooming all the way in was that his track readings bounced back and forth across the trail constantly, forcing me to smooth point after point to ensure they were all on the trail that appeared on the map. (I’m not sure what RunGo’s base map is, or where it got the trail markings, but they generally matched up with what was on the ground.) By the time I had finished smoothing the entire course to the marked trail, it was back to that 13.1 miles I’d initially estimated from OnTheGoMap. Various other GPSes also got different numbers: for instance:
In other words, my sense is that we can trust OnTheGoMap’s algorithm to do the right thing and come up with an accurate distance. The question is if the lines it’s putting down to track roads and trails match up with what runners will do in reality. Similarly, GPSes tend to fall down when following the exact trail too, due to reception problems from trees and terrain, coupled with tight turns where the GPS may not catch up with you instantly.
Of course, it doesn’t matter much for trails. Even in a race, no one really cares about the precise distance because the terrain and conditions affect times so significantly, and there’s no comparison against other trail races of the same distance. In road or cross-country races, when the goal is to have a course of a specific distance, the only real solution is to wheel the course.
And for training, whatever. Just go with what the GPS watch says—it’s good enough.
I’ve read through this thread and thought I’d add some notes on GPS watches and trail running, based on my experience with various watches and phones over the years.
Plotting a route using an app like RunGo is probably a lot more accurate that what you record on a GPS, assuming you smooth out the route to match the trail as it appears in the map. Like Adam said, distance is measured inaccurately because it doesn’t account for tight turns, and sometimes the GPS signal is hindered by clouds or tree cover. GPS does not record data points continuously. Instead, it records your location over a series of intervals (i.e. every 1 second or every 5 seconds) and then makes educated guesses to fill in the gaps. The higher the frequency of the recording, the more accurate the distance and pace will be, but this drains the battery quicker and fills up the device’s internal memory sooner, as it is recording a larger data file.
In general, dedicated GPS devices, such as a running watch, record more accurately than phones. This is because the GPS is the watch’s main function so the manufactures use the best technology possible for a given retail price point. On a smart phone the GPS is one of hundreds of features so the manufacturers are less concerned with high level GPS accuracy. The difference in accuracy is less of a factor running in roads or an outdoor track because there are fewer turns and less tree cover to weaken the GPS signal.
Re my GPS track for the Lick Brook Challenge course: my Suunto 9 GPS watch measured a lot more accurately during the first year I owned it. A software update in 2020 somehow caused it to consistently measure about 5% long on trails. Based on mapping software and prior runs on those trails with my older watch, I think the actual distance is around 13.3-13.5 miles. Nancy’s new Monster course is also very close to 13.1, despite measuring 14 when I ran it a month ago.
Lastly, if you’re interested (as I am) in using a watch to track vertical gain on your runs, a barometer is much more accurate than an altimeter, but it also adds to the retail price.
Any questions, let me know and I’ll answer best I can!
@SarahG Avenza and Gaia both work well if you’ll be running someplace without a reliable cell signal. Both apps allow you to load a .pdf of a trail map into the app, then display it with an overlay while the phone’s GPS shows your lactation in the map. It’s best to practice and get familiar with the features before using it in the woods so you don’t risk getting lost. Also, if you’re relying on the app and map for navigation, it’s best to use your phone in airplane mode so you don’t risk draining the battery and getting lost with no map (which I’ve done before!)